Please welcome back Frank Indiviglio for another fascinating species profile.
Perhaps because of its lack of color, the blind cave fish
, Astyanax fasciatus mexicanus
, does not receive nearly the attention it warrants. This 5 inch-long fish was first discovered by Salvador Coronado, a young employee of Mexico’s Department of Fisheries, and it was he who later led a New York Aquarium sponsored expedition to collect the bizarre creatures. The species’ entry into the aquarium world’s consciousness is recounted by expedition member William Bridges, of the Bronx Zoo, in his initial report – “…at three o’clock on a March afternoon, a thousand feet inside the cave, two of us dragged a net out of the black water and revealed a dozen little flopping white fish…”. Amazingly, fish from that first collection appeared in three distinct forms – with normal eyes, with eyes of reduced size and without eyes. Fortunately for we fish enthusiasts, captive-born blind cave fish eventually found their way into the pet trade.
The blind cave fish is found in only one cave, La Cueva Chica (the “Little Cave” – the entrance is only 15 feet wide) near Pujal, in San Lois Potosi, Mexico (related species have since been found in other caves). This fact alone should grant it special status among fish keepers, but there is much more to distinguish it – including a rare glimpse at fish adaptation in progress. Apparently, fish with normally developed eyes live in a nearby river, the Rio Tampaon, and are regularly swept into the cave by the current. There, deprived of light and the need for sight, the eyes degenerate. As time goes on, their descendents are born with gradually more reduced eyes, until the eyeless form emerges. Although I have not read evidence of it, I imagine that inter-breeding with eyeless fish already in the cave may hasten the process.
Fish in pools nearest the cave’s entrance rely upon flies, spiders and other invertebrates for food, while those deep inside subsist upon bat guano, dead bats and, I would venture a guess, fleas and other invertebrates that fall from the bats’ fur.
Check back on Friday to read the rest of this article.